Lux junior 2015 25. bis 27.9.15 Dörnfeld

Road Surface Reflection Properties of Typical for Bulgaria Pavement Materials Iva Petrinska 1, Dilian Ivanov 1, Dimitar Pavlov1, Kamelia Nikolova 1 Technical University of Sofia Abstract The luminance of asphalt road surfaces is a function of the horizontal illuminance and the reflection properties of the surface at any point. The reflection properties of the road surfaces depend on their physical condition, age and type (components and roughness of the surface). The current standards and recommendations are based on the luminance of the road surface and its distribution along the road. This distribution depends to a great degree on the reflection properties of the road. The existing standard tables of reflection of the road surfaces are not valid for all the road conditions. The cracked and old surfaces are typical for Bulgaria, which means that the reflection tables, given by the standard will not lead to a proper design of street lighting systems. The aim of the current investigation is description of the real reflectance characteristics of typical for Bulgaria road surfaces, according to their age, fracture of the materials and condition. Keywords: road surface reflectance properties, reflection characteristics of surfaces

1. INTRODUCTION The safety of the road traffic at nighttime is decided by the illumination of the road surface. With proper lighting, people and objects on the road are made visible, thus ensuring their detection by drivers. The contemporary quality criteria for street lighting require minimum luminance of the roadway ensured, matching the type of the illuminated street. As it is well known the calculation of the average luminance on a road with a given geometry of the lighting installation is possible only if the reflection characteristics of the road surface are known. Road lighting standards in Europe give values of the average road surface luminance, overall luminance uniformity ratio, longitudinal uniformity ratio, disability glare and surround ratio [1, 2, 3, 4]. The luminance of a given point on the road can be calculated if the luminous intensity in the direction of the point and the reflection characteristics of the road surface are known. The luminous intensity depends on the luminaires’ light distribution curve and their luminous flux. The road surface reflection is a function of the physical state of the road and its nature as well as on the direction of its illumination and the conditions of observation [5]. The different pavements can have different reflection characteristics which depend on the texture of the surface and its age, materials included in the pavement, binding materials and paving method. Reflection characteristics change with the weather conditions and

Lux junior 2015 25. bis 27.9.15 Dörnfeld

also alter with the change of their physical state (when holes or cracks occur, also when they are worn out). With the change of the reflection properties of the road surfaces their luminance also changes. The distribution of the luminance L on the roadways, illuminated by stationary lighting systems is determined by the arrangement and height of the poles, light distribution of the luminaire and reflection properties of the pavement. It can be calculated using the formula: L = q*Eh

(1)

where q is luminance coefficient which is defined by four angles α – the angle of observation from the horizontal plane, β – the angle between vertical plane of light incidence and vertical plane of observation, γ – the angle of light incidence from the upward vertical, δ – the angle between the road axis and the vertical plane of observation [6]. The angle δ is usually neglected and the angle α is considered constant 1° (because of the viewing height of the drivers 1.5m and the important for detecting obstacles area of 60 – 160 m ahead of the driver) [6]. The reflection characteristics of road surfaces are given by set of reduced luminance coefficients r, arranged in tables for different combinations of β and γ angles: r = q*cos3γ

(2)

These tables give description of the reflection characteristics of roadways. In order to obtain general information on the road surface reflection properties, the general illuminance coefficient and specular factors S1 and S2 are introduced. They can be defined using the following equations: =

∫

(3)

Where Ω is the solid angle, from the point source on the surface, containing all directions from which light is incident that are considered in the averaging process. The specular factor S1 is a ratio between the reduced luminance coefficients r (0,2) and r(0,0), that are generally large respectively for specular and diffuse reflection: 1=

( , ) ( , )

(4)

The specular factor S 2 is defined as follows: 2=

( , )

(5)

These properties of the road surfaces are unique and change with time. They can be measured for real roads but this is a hard work and it is rarely done. CIE has defined rtables for road surfaces, classified according to their reflectance properties [5, 7]. The standard r tables date back from the 1960s, so actualization has to be considered. Also the fractures of the pavement materials, used in the different countries differ, which will also lead to changes in their reflectance properties.

Lux junior 2015 25. bis 27.9.15 Dörnfeld

The CIE publication 30-2 gives a classification of the road surfaces into four representative classes – R1, R2, R3, R4 with standardized r-tables [5]. Another classification introduces the C-classes – C1 and C2 that are also generalized and standardized [7]. Based on the class and the Q0 value of the road surface, the luminance of the road can be calculated and the street lighting system designed. Table 1 Classification of road surfaces according to CIE 30-2, 1982 and CIE 66, 1984 Class R1 R2 R3 R4

S1 limit S1